The main goal of this research proposal is to provide new knowledge regarding the basic mechanism involved in the degradation of plasma triglyceride-rich lipoproteins. Although adipose tissue and post-heparin plasma lipoprotein lipase(s) are more directly involved in the metabolism of triglyceride-rich lipoproteins, human milk is an abundant source of one of the lipoprotein-lipases, i.e., the C-II-activated lipoprotein-lipase (LPLC-II). Since there is a close antigenic relationship between human milk and plasma LPLC-II, the more accessible milk enzyme will be used as a model for studying the chemical, physical, immunologic and functional properties of this group of lipolytic enzymes. The specific aims of this study include 1) isolation and purification of human milk LPLC-II, 2) determination of physical, chemical and immunologic properties of human milk LPLC-II, 3) studies on the kinetic properties of human milk LPLC-II, 4) development of a method for a concurrent measurement of activities and protein concentrations of post-heparin plasma lipoprotein lipases (LPLC-I and LPLC-II) and triglyceride lipase, and 5) studies on the lipolysis of triglyceride-rich lipoproteins by human milk LPLC-II and the chemical characterization of lipoprotein degradation products. The newly developed methodology for concurrent measurement of post-heparin plasma lipoprotein lipases and triglyeride lipase will be applied to a study of plasma lipase system in normolipidemic subjects and patients with various types of hypo- and hyperlipoproteinemias. These studies may clarify the role of lipoprotein lipase(s) in the catabolic conversion of triglyceride-rich to triglyceride-poor lipoproteins, provide new information about the pathogenesis of hypertriglyceridemia, and, in general, contribute to a better understanding of lipid transport processes.